Enable prepayment allocation to the first upcoming instalment on the revolving credit account. Even though installment does not exist at the time of prepayment, actual installment calculation could check what was accumulated prepaid amount after previous installment.
On the revolving credit account clients are allowed to make prepayment, however this does not affect upcoming installment. If the client pays even a single day before the due date, installment will still become due in the full amount. Described solution would allow early payments.